Dystonic neck muscles show a shift in relative autospectral power during isometric contractions

Objective: To identify effects of a deviant motor drive in the autospectral power of dystonic muscles during voluntary contraction in cervical dystonia patients. Methods: Submaximal (20%) isometric head-neck tasks were performed with the head fixed, measuring surface EMG of the sternocleidomastoid, splenius capitis and semispinalis capitis in CD patients and controls. Autospectral power of muscle activity, and head forces was analyzed using cumulative distribution functions (CDF). A downward shift between the theta/low alpha-band (3-10 H z) and the high alpha/beta-band (10-30 Hz) was detected using the CDF10, defined as the cumulative power from 3 to 10 Hz relative to power from 3 to 30 Hz. Results: CDF10 was increased in dystonic muscles compared to controls and patient muscles unaffected by dystonia, due to a 3-10 Hz power increase and a 10-30 Hz decrease. CDF10 also increased in patient head forces. Conclusions: Submaximal isometric contractions with the head fixed provided a well-defined test condition minimizing effects of reflexive feedback and tremor. We associate shifts in autospectral power with prokinetic sensorimotor control. Significance: Analysis of autospectral power in isometric tasks with the head fixed is a promising approach in research and diagnostics of cervical dystonia